A star like our Sun exists in a state of equilibrium: its own gravity tries to pull the Sun's mass inward toward the center, but the outward radiation force due to nuclear fusion (which burns hydrogen...A star like our Sun exists in a state of equilibrium: its own gravity tries to pull the Sun's mass inward toward the center, but the outward radiation force due to nuclear fusion (which burns hydrogen fuel to create helium, causing the Sun to shine) is pushing outward. For a bigger star (4-8 up to about 10-15 solar masses), the star's gravity is strong enough to actually collapse the atoms in what would have been a white dwarf at the end of the star's life.
